I use a commercial Asterisk-based SIP provider for my business. I'm going through the process of acquiring hearing aids, and it may be smartest for me to stream telephone audio from my provider directly to my aids via bluetooth and a softphone (I spent a lot of time on the phone). I could conceivably use my Android handset, but it seems k,ind of clunky. I used to use X-Lite under Windows, but the Linux version is very rough comparatively. I've also tried Xoiper, but find the interface pretty rough. I want something that's close to a phone dialing and usage wise.

Counterpath makes Bria and Eyebeam, which are more contemporary then X-Lite, but there is apparently no way to try them out (I would be open to buying one if that made sense).

I hadn't seen this one before, but installed easily and appears to work well. Has the added benefit of being able to to sync to the Gnome address book (which can sync to Gmail for contacts).
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KendorDec 28 '10 at 0:05

You can try Jitsi (http://www.jitsi.org). I use this in a corporate environment to connect to Openfire Server (Jabber server using XMPP) and also to a VOIP Server (Asterisk based - PIAF software). Audio, video and screen sharing work very nicely.

Jitsi allows you to sign in various accounts at the same time. Unified communications in the real sense

I played around with many SIP Softphones and by far Linphone was the most reliable. It is extremely reliable in terms of audio and video throughput. It may be a little choppy wrt to the UI, even though recently they've made progress on that, but this is just a small nitpick compared to the technical reliability. One added benefit is the impressive platform support:

Linphone has been launched in 2001. It was the very first open source application using SIP software on Linux. For more than 10 years, a lot of improvements have been done and Linphone has been ported on the main desktop, mobile and web platforms:

Belledonne Communications company is developing and maintaining Linphone and related projects. It offers commercial assistance and licensing for companies using or integrating Linphone within their products.